The present invention relates to so-called automatic grounding means for electrical wiring devices and, more specifically, to that class of automatic grounding means wherein a metallic clip is affixed to the mounting strap or yoke of the wiring device for contact by a screw which connects the device to a wall-mounted box.
Wiring devices such as switches or plug-receiving receptacles must be properly grounded in order to protect the user against dangerous electrical shorts that might occur, for example, in the wiring of equipment connected to the device. Such wiring devices are conventionally mounted in metal boxes which are attached to structural members at ground potential. Metal screws extending through oversized openings (i.e., larger than the screw diameter) in each end of a mounting strap or yoke serve to connect the wiring device to the box. Thus, the device is effectively grounded by the screw providing a low resistance electrical connection between the yoke and the mounting box.
It is sometimes found in such installations that the mounting screw is not always in firm contact with the yoke, due to the necessity of providing oversized openings in the yoke ends. This may be due to a slight misalignment in the position of the yoke as a face plate is mounted over the wiring device, or may be caused by other factors, even though the screw is initially in the desired contact with the yoke. In any case, the result is that a good grounding connection is not always provided for the yoke of the wiring device, and therefore for electrical appliances and the like which are connected thereto.
One approach to the foregoing problem has been to attach so-called automatic grounding clips to the yoke in order to insure that the necessary grounding connection is made. Typical examples of such clips are found, for example, in U.S. Pat. Nos. 3,432,793, 3,639,884, 3,723,941, 3,728,468, 3,757,268, 3,885,847 and 3,963,292. Of these patents, probably those bearing the closest relationship to the present invention are U.S. Pat. Nos. 3,432,793 and 3,639,884 of Muska et al., and Drapkin, respectively. In the Muska et al. design, a pair of wires extend across the screw-receiving openings in the yoke and are welded to the yoke. The wires are spaced by a distance less than the diameter of the mounting screw which is thus in contact with both wires when passing therebetween, assuring a low resistance ground path from the yoke to the wires, screw and box. Drapkin provides a single wire extending across the screw-receiving opening behind the strap. One end of the wire is anchored within a small aperture and the other end is free to slide in a slot extending inwardly from an edge of the strap.
It is a principal object of the present invention to provide an automatic grounding clip of simple and economical design which can be quickly and easily assembled with an electrical wiring device.
A more general object is to provide a wiring device yoke and grounding clip in a novel and improved configuration and relationship.
Another object is to provide means for insuring a ground path between the yoke of a wiring device and a mounting box through the screws which connect the two, such means being assembled with the yoke in a secure manner, whereby inadvertent disconnection is unlikely, yet requiring no permanent connection operations such as welding or brazing.
A further object is to provide an automatic grounding clip for mounting on the yoke of a wiring device in two forms which are respectively adapted for automatic or manual assembly of the clip with the yoke.
Other objects will in part be obvious and will in part appear hereinafter.